Achieving Bright Mechanoluminescence in a Hydrogen-BondedOrganicFramework by PolarMolecular Rotor Incorporation

Abstract

Luminescent hydrogen-bonded organic frameworks (HOFs) have attracted increasing attention due to their corresponding luminescence that enables readily visualization of structural dynamics. HOFs with the mechanoluminescence (ML) property can emit light without photon excitation and are greatly attractive for advanced applications, but research in this area has been limiting. Herein, we report the first example of an ML-active flexible HOF with permanent porosity, named 8PCOM, assembled from polar molecular rotors with an aggregation-induced emission property.When responding to different solvent vapors, reversible structural transformations between ML-active and -inactive 8PCOM frameworks occur, including a single-crystal-to-single-crystal (SCSC) transformation. Thus, guest-induced breathing behaviors are mainly attributed to phenyl rotations of polar molecular rotors induced by external stimuli. During reversible structural transformations of various 8PCOM frameworks with different pores, the significant ML property is achieved successfully through supramolecular dipole moment regulation. Upon mechanical force, bright emission of the ML-active 8PCOM framework is observed without UV irradiation, and the ML-active crystals can be easily prepared and regenerated. This work not only provides a valuable strategy for engineering future multifunctional HOFs but also enriches the types and applications of existing luminescent porous materials.